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DAEMON(3) FreeBSD Library Functions Manual DAEMON(3)
NAMEdaemon -- run in the background
LIBRARY
Standard C Library (libc, -lc)
SYNOPSIS#include <stdlib.h>
intdaemon(intnochdir, intnoclose);
DESCRIPTION
The daemon() function is for programs wishing to detach themselves from
the controlling terminal and run in the background as system daemons.
Unless the argument nochdir is non-zero, daemon() changes the current
working directory to the root (/).
Unless the argument noclose is non-zero, daemon() will redirect standard
input, standard output, and standard error to /dev/null.
RETURN VALUES
The daemon() function returns the value 0 if successful; otherwise the
value -1 is returned and the global variable errno is set to indicate the
error.
ERRORS
The daemon() function may fail and set errno for any of the errors speci-
fied for the library functions fork(2) and setsid(2).
SEE ALSOfork(2), setsid(2), sigaction(2)HISTORY
The daemon() function first appeared in 4.4BSD.
CAVEATS
Unless the noclose argument is non-zero, daemon() will close the first
three file descriptors and redirect them to /dev/null. Normally, these
correspond to standard input, standard output, and standard error. How-
ever, if any of those file descriptors refer to something else, they will
still be closed, resulting in incorrect behavior of the calling program.
This can happen if any of standard input, standard output, or standard
error have been closed before the program was run. Programs using
daemon() should therefore either call daemon() before opening any files
or sockets, or verify that any file descriptors obtained have values
greater than 2.
The daemon() function temporarily ignores SIGHUP while calling setsid(2)
to prevent a parent session group leader's calls to fork(2) and then
_exit(2) from prematurely terminating the child process.
FreeBSD 10.1 June 9, 1993 FreeBSD 10.1